amd 64 video processing problem

I have recently upgraded to an AMD 64 3200 Venice on an Abit AX8 board and an Asus Nvidia 6600GT card. Since this I have not been able to process any video files for burning films etc or even to change the file type (avi tompeg for example). Ihave uppped the BIOS on the board and tried many other video progs. I usually use DVDSanta. the video file will play on the PC OK. It is running at standard speeds (no OC) and has 1gb of ram. Has anyone any Ideas that could solve this? I would be most grateful. Fuzz.

yes I have tried the windows 64 and standard xp (2) the memory and drives dvd etc are the ones used prior to the upgrade also only the processor m/b and video card have been replaced and I use a 550 watt psu